Lawrence Berkeley National Laboratory

One of the greatest challenges in biology is to understand the interaction between genotype and environment to determine the fitness of an organism. With the recent advances in genome sequencing and high-throughput genomic technologies, it is possible now to link sub-cellular molecular/metabolic processes with the population-level processes, functions and evolution. Sulfate reducing bacteria Desulfovibrio vulgaris Hildenborough is an ideal model environmental organism to address such fundamental questions. In this study, a long-term evolution experiment was carried out under controlled laboratory conditions for D. vulgaris. The salt tolerance was tested periodically bymonitoring the growth of cell lines on LS4D + 250 mM NaCl. The results demonstrated that the adaptation to salt stress was a dynamic process. Enhanced salt tolerance to higher salt (250 mM NaCl) was observed at 300generations and it became more obvious with the increase of generations. De-adaptation of cell lines by removal of salt stress at 500, 1000, and 1200 generation cell lines did not affect the increased salt tolerance, indicating that the observed phenotype changes was due to genetic changes instead of physiological adaptation. Furthermore, results from the de-adaptation experiment suggest the dynamic trend of genetic adaptation and the genetic mutation may become stable at 1000 generations, which was also confirmed by the microarray data from 500 and 1000 generation samples. hmcF-E-D-C-B-A, rrf2-rrfl, lysA-2lysX and DVU3290-3291-3292 (glutamate synthase) were examples of significantly up-regulated polycistronic operons in long-term stressed lines. Whole genome sequencing of selected colonies is underway to identify the benefical genetic mutations.